The interpolation problem for a set of three fat points in $mathbb{P}^1timesmathbb{P}^1$

This is an appendix to the recent paper of Favacchio and Guardo. In these notes we describe explicitly a minimal bigraded free resolution and the bigraded Hilbert function of a set of 3 fat points whose support is an almost complete intersection (ACI) in $mathbb{P}^1timesmathbb{P}^1.$ This solve the interpolation problem for three points with an ACI support.